Agricultural lands are hot-spots for annual runoff polluting the southern Great Barrier Reef lagoon

The world’s largest coral reef ecosystem, the Great Barrier Reef (GBR), continues to be degraded from land-based pollution. Information about the source of pollutants is critical for catchment management to improve GBR water quality. We report here on an 11-year source to sea study of pollutant delivery in runoff from the Fitzroy River Basin (FRB), the largest GBR catchment. An innovative technique that relates land use to pollutant generation is presented. Study results indicate that maximum pollutant concentrations at basin and sub-catchment scales are closely related to the percentage area of croplands receiving heavy rain. However, grazing lands contribute the majority of the long-term average annual load of most common pollutants. Findings suggest improved land management targets, rather than water quality targets should be implemented to reduce GBR pollution. This study provides a substantial contribution to the knowledge base for the targeted management of pollution ‘hot-spots’ to improve GBR water quality.     

Water quality and coral bleaching thresholds: Formalising the linkage for the inshore reefs of the Great Barrier Reef, Australia

The threats of wide-scale coral bleaching and reef demise associated with anthropogenic climate change are widely known. Here, the additional role of poor water quality in lowering the thermal tolerance (i.e. bleaching ‘resistance’) of symbiotic reef corals is considered. In particular, a quantitative linkage is established between terrestrially-sourced dissolved inorganic nitrogen (DIN) loading and the upper thermal bleaching thresholds of inshore reefs on the Great Barrier Reef, Australia. Significantly, this biophysical linkage provides concrete evidence for the oft-expressed belief that improved coral reef management will increase the regional-scale survival prospects of corals reefs to global climate change. Indeed, for inshore reef areas with a high runoff exposure risk, it is shown that the potential benefit of this ‘local’ management imperative is equivalent to ∼2.0-2.5 °C in relation to the upper thermal bleaching limit; though in this case, a potentially cost-prohibitive reduction in end-of-river DIN of >50-80% would be required. An integrated socio-economic modelling framework is outlined that will assist future efforts to understand (optimise) the alternate tradeoffs that the water quality/coral bleaching linkage presents.     

Circulation in the Great Barrier Reef Lagoon using numerical tracers and in situ data

Numerical hydrodynamic models of the northeastern Queensland shelf, forced by regional winds and modelled boundary currents in the northern Coral Sea, are used to provide improved estimates of general flow trajectories and water residence times within the Great Barrier Reef (GBR) shelf system. Model performance was checked against a limited set of current metre records obtained at Lark Reef (16°S) and the Ribbon Reefs (15.5°S). Estimates of water parcel trajectories are derived from a series of numerical tracer experiments, with daily releases of neutrally buoyant, un-reactive particles at 320 sites along the coast between Cape York (10.7°S) and Hervey Bay (25°S). Flow trajectories and residence times for tracer particles introduced to the GBR lagoon in the southern—ca. 22°S, central—19°S, and northern reef—14°S are emphasised. For purposes of the analysis, the year was divided into two seasons based on mean alongshore current direction. Most coastal sourced tracers entering the central GBR lagoon between 16° and 20°S during the northward-current season (January–August) primarily encounter the outer-shelf reef matrix after exiting the lagoon at its northern “head” (nominally 16°S), after 50–150 days. Up to 70% of tracer particles entering in the southward-current season (August–December) eventually crossed the lagoon to the outer-shelf reef matrix, with median crossing times between 20 and 330 days. During favourable wind conditions, tracers introduced at the coast may move rapidly across the lagoon into the reef matrix. The tracer experiments indicate that most coastal-sourced tracers entering the GBR lagoon remain near the coast for extended periods of time, moving north and south in a coastal band. Residence times for conservative tracer particles (and implied residence times for water-borne materials) within the GBR shelf system ranged from ca. 1 month to 1 year—time frames that are very long relative to development times of planktonic larvae and cycling times for nutrient materials in the water column, implying they are transformed long before reaching the outer reef matrix.     

Pesticide and Herbicide Residues in Sediments and Seagrasses from the Great Barrier Reef World Heritage Area and Queensland Coast

Pesticides and herbicides including organochlorine compounds have had extensive current and past application by Queensland's intensive coastal agriculture industry as well as for a wide range of domestic, public health and agricultural purposes in urban areas. The persistent nature of these types of compounds together with possible continued illegal use of banned organochlorine compounds raises the potential for continued long-term chronic exposure to plants and animals of the Great Barrier Reef. Sediment and seagrass samples were collected from 16 intertidal and 25 subtidal sampling sites between Torres Strait and Townsville, near Mackay and Gladstone, and in Hervey and Moreton Bays in 1997 and 1998 and analysed for pesticide and herbicide residues. Low levels of atrazine (0.1–0.3 μg kg⁻¹), diuron (0.2–10.1 μg kg⁻¹), lindane (0.08–0.19 μg kg⁻¹), dieldrin (0.05–0.37 μg kg⁻¹), DDT (0.05–0.26 μg kg⁻¹), and DDE (0.05–0.26 μg kg⁻¹) were detected in sediments and/or seagrasses. Contaminants were mainly detected in samples collected along the high rainfall, tropical coast between Townsville and Port Douglas and in Moreton Bay. Of the contaminants detected, the herbicide diuron is of most concern as the concentrations detected have some potential to impact local seagrass communities.     

Sediment resuspension events within the (microtidal) coastal waters of Thermaikos Gulf, northern Greece

High-frequency flow, pressure and suspended sediment concentration (SSC) measurements are presented from the Paralia-Katerinis coastal area, in Thermaikos Gulf. The data were collected along a cross-shore transect, between the 6 and 12 m water depth contours. The relative importance of wave- and tidally-induced resuspension is examined. Resuspension events are shown to be dominated by wind-generated waves, especially under storm conditions. Some evidence is provided for tidal resuspension, but the overall impact of this process is minimal, compared to wave resuspension. Such resuspension, under storm conditions, increased the SSC levels in the waters of the nearshore zone to 35 mg/l; this is a >15-fold increase over the ambient levels (1–2 mg/l) of turbidity.     

A simple and inexpensive turbidity meter for the estimation of suspended sediment concentrations

The relatively high cost of commercially available turbidity meters has inhibited detailed and intensive research on spatiotemporal patterns of suspended sediment transport. We describe here the electronic and physical design of an inexpensive turbidity sensor which is easy to construct, simple to interface with portable millivolt meters, dataloggers, computers, or chart recorders, consumes exceptionally small currents, and is robust and reliable. the very low individual cost allows a large number of sensors to be distributed throughout the water body of interest to facilitate turbidity mapping. Turbidity profilers to detect vertical or lateral turbidity changes in rivers, lakes, estuaries, or near-shore zones are also shown to be feasible. Test data are presented from a highly turbid glacial river in southern Iceland.     

Water Quality in the Great Barrier Reef World Heritage Area: Past Perspectives, Current Issues and New Research Directions

Elevated sediment and nutrient concentrations have long been regarded as the pre-eminent water quality threats to the Great Barrier Reef, with the potential risk posed by other pollutants such as heavy metals, persistent chlorohydrocarbons, PCBs and petroleum related compounds considered to be of lesser consequence. However, the management focus on these latter types of pollutants has recently shifted to acknowledge the potential impact posed by diuron, dioxins, dieldrin, and mercury and cadmium concentrations detected in sediments and biota along the Great Barrier Reef and southern Queensland coastline. In general, these threats originate from areas dominated by intensive cropping agriculture and are exacerbated by high rainfall and erosion rates in the wet tropics region of the Queensland coast. Maintenance of long-term monitoring programmes, which utilize innovative data acquisition techniques will enable assessment of change in environmentally relevant pollutant concentrations over time. However, improved land management practices, which include an immediate minimization of vegetation clearance and responsible use of pesticides and fertilizers in Queensland are essential if water quality in the Great Barrier Reef World Heritage Area is to be maintained and protected.     

Deposition, mineralization, and storage of carbon and nitrogen in sediments of the far northern and northern Great Barrier Reef shelf

The flow of carbon and nitrogen in sediments of the far northern and northern sections of the Great Barrier Reef continental shelf was examined. Most of the organic carbon (81–94%) and total nitrogen (74–92%) depositing to the seabed was mineralized, with burial of carbon (6–19%) and nitrogen (8–20%) being proportionally less on this tropical shelf compared with other non-deltaic shelves. Differences in carbon and nitrogen mineralization among stations related best to water depth and proximity to river basins, with rates of mineralization based on net ∑CO₂ production ranging from 17 to 39 ( mean=23) mmol C m⁻² d⁻¹. The overall ratio of O₂:CO₂ flux was 1.3, close to the Redfield ratio, implying that most organic matter mineralized was algal. Sulfate reduction was estimated to account for ≈30% (range: 6–62%), and denitrification for ≈5% (range: 2–13%), of total C mineralization; there was no measurable CH₄ production. Discrepancies between ∑CO₂ production across the sediment–water interface and sediment incubations suggest that as much as 5 mmol m⁻² d⁻¹ (≈25% of ∑CO₂ flux) was involved in carbonate mineral formation. Most microbial activity was in the upper 20 cm of sediment. Rates of net NH₄⁺ production ranged from 1.6 to 2.7 mmol N m⁻² d⁻¹, with highly variable N₂ fixation rates contributing little to total N input. Ammonification and nitrification rates were sufficient to support rapid rates of denitrification (range: 0.1–12.4 mmol N m⁻² d⁻¹). On average, nearly 50% of total N input to the shelf sediment was denitrified. The average rates of sedimentation, mineralization, and burial of C and N were greater in the northern section of the shelf than in the far northern section, presumably due to higher rainfall and river discharge, as plankton production was similar between regions. The relative proportion of plankton primary production remineralized at the seafloor was in the range of 30–50% which is at the high end of the range found on other shelves. The highly reactive nature of these sediments is attributed to the deposition of high-quality organic material as well as to the shallowness of the shelf, warm temperatures year-round, and a variety of physical disturbances (cyclones, trawling) fostering physicochemical conditions favorable for maintaining rapid rates of microbial metabolism. The rapid and highly efficient recycling of nutrients on the inner and middle shelf may help to explain why the coral reefs on the outer shelf have remained unscathed from increased sediment delivery since European settlement.     

A meta‐analysis of reef island response to environmental change on the Great Barrier Reef

Reef islands on the Great Barrier Reef are influenced by a range of environmental factors. A meta‐analysis of 103 islands is presented to express variation in island size (area and volume) as a function of latitudinal and cross shelf gradients in regional oceanographic factors (exposure to incident waves, tidal range and tropical cyclone frequency) and local physical factors (position on the shelf, area, length and depth of supporting reef platform, vegetative cover). Models performed well for unvegetated sandcays (R² = 0.89), vegetated sandcays (R² = 0·72) and low wooded islands (R² = 0.78), with a moderate level of variation explained when all islands were simultaneously regressed (R² = 0.58). Future island dynamics were simulated for anticipated changes in cyclone regime, wave activity and sea level. For 38 islands mapped on the 1973 Royal Society and Universities of Queensland Expedition to the Northern Great Barrier Reef, change over the same 22 year period (1973–1995) was determined and the relative magnitude of observed and modelled changes was compared and found to be consistent through rank correlation analysis (Γ = 0.84 for unvegetated sandcays, Γ = 0.81 for vegetated sandcays). Simulations of island area or volume change from 2000 to 2100 indicated that under a 30% decrease in tropical cyclone activity, unvegetated sandcays continue to accrete at a lower rate, whereas all island types erode under a 38% increase in tropical cyclone activity. Vegetated sandcays initially accrete at higher levels of cyclone activity, entering an erosive state with a 60% increase in activity. Low wooded islands are unresponsive to environmental changes modelled. A sensitivity analysis of vegetated and unvegetated sandcays indicated that the presence of vegetation increases the tropical cyclone activity threshold at which islands begin to erode. Greatest sedimentary losses occur within the central band of high cyclone activity between Cooktown and Mackay. Copyright © 2015 John Wiley & Sons, Ltd.     

Quantifying Inputs of Pesticides to the Great Barrier Reef Marine Park – A Case Study in the Herbert River Catchment of North-East Queensland

The Great Barrier Reef Marine Park (GBRMP) is an ecosystem whose ecological features are recognized internationally. There is a need to evaluate the impacts of historical and contemporary changes in land use on the GBRMP. This paper quantifies pesticide inputs in the Herbert River catchment of North Queensland in the context of changes in land use over the last 100 years. We show that three major phases of rural land use and land cover change have occurred, with large areas of native vegetation converted to agricultural production. The increase in agricultural land has seen a corresponding increase in the area receiving pesticides. We present data showing application histories for organochlorine, organophosphate, phenoxy, triazine, urea, mercurial and azole group pesticides. While the fate of these pesticides in aquatic and marine systems is largely unknown, these trends pose a significant challenge for agricultural industries in complying with the principles of ecologically sustainable development (ESD).     

Preliminary evaluation of the occurrence of herbicides and PAHs in the Wet Tropics region of the Great Barrier Reef, Australia, using passive samplers

The proximity of the Great Barrier Reef (GBR) Marine Park to areas of intensive agriculture and increasing urbanisation places the park under potential threat of contamination by land-based pollutants. Passive samplers were deployed at inshore reef and river mouth sites in the Wet Tropics region of the GBR during a dry and a wet season to measure levels of land-based organic pollutants in this environment. Two types of passive sampling devices were deployed: (i) a polar sampler, which can be used to monitor polar herbicides and (ii) semipermeable membrane devices (SPMDs) which sequester more hydrophobic compounds (e.g. PAHs, chlorpyrifos). Herbicides (diuron, simazine, atrazine, hexazinone and/or flumeturon) were detected at low concentrations (ng L⁻¹) at all sites sampled and in both seasons. Chlorpyrifos was not detected while PAHs were present in SPMDs at levels below limits of detection. The results show that the GBR environment does contain low levels of organic pollutants and that passive sampling provides a sensitive monitoring tool for measuring waterborne organic pollutants.     

Numerical investigation of the factors influencing the vertical profiles of current,salinity, and SSC within a turbidity maximum zone

The flow-sediment interaction plays a considerable role on the vertical (internal) profiles of current,salinity and suspended sediment concentration (SSC) within a turbidity maximum zone (TMZ).Numerical modeling provides valuable insights into the complex estuarine physical processes.By combining numerical modeling with field observations,the influencing factors of fine sediment dynamics within the TMZ of Yangtze Estuary have been explored in this study.Firstly,during the neap tide,the measured data present that the current is too weak to break the density stratification,and the vertical flow structure is effectively altered.Secondly,a three-dimensional numerical model based on the Delft3D has been developed and a range of numerical sensitivity analyses were carried out to distinguish the dominant mechanisms and physical processes responsible for the phenomena observed from the measurement data.The numerical investigation highlights the following findings.(1) The vertical profile of currents within the TMZ is largely affected by saltwater intrusion,especially during lower currents when the baroclinic pressure gradient can significantly reshape the local vertical profiles of velocity.(2) The baroclinic effects are primarily determined by the stratification of salinity.(3) In addition to salinity,SSC also influences the local density stratification when its contribution to fluid density is comparable to that of salinity.(4) The settling velocity determines the overall sediment distribution and vertical profiles of the SSC in the water column.The SSC-dependent settling velocity (including the flocculation-induced acceleration and hindered settling deceleration phases) affects the longitudinal movement of the sediments.(5) The vertical profiles of current,salinity and SSC within the TMZ are highly associated with the turbulence determined by the model.The approach to modulate the vertical eddy viscosity in the model,based on the empirical dependency between Rig and Prt,may lead to a numerical instability in the stratified flow.In order to improve the stratification of SSC,additional turbulence damping effect is suggested to be implemented in the model.     

Transforming management of tropical coastal seas to cope with challenges of the 21st century

Over 1.3 billion people live on tropical coasts, primarily in developing countries. Many depend on adjacent coastal seas for food, and livelihoods. We show how trends in demography and in several local and global anthropogenic stressors are progressively degrading capacity of coastal waters to sustain these people. Far more effective approaches to environmental management are needed if the loss in provision of ecosystem goods and services is to be stemmed. We propose expanded use of marine spatial planning as a framework for more effective, pragmatic management based on ocean zones to accommodate conflicting uses. This would force the holistic, regional-scale reconciliation of food security, livelihoods, and conservation that is needed. Transforming how countries manage coastal resources will require major change in policy and politics, implemented with sufficient flexibility to accommodate societal variations. Achieving this change is a major challenge – one that affects the lives of one fifth of humanity.     

Integrating water management,habitat modelling and water quality at the basin scale and environmental flow assessment: case study of the Tormes River,Spain

Abstract

Multidisciplinary models are useful for integrating different disciplines when addressing water planning and management problems. We combine water resources management, water quality and habitat analysis tools that were developed with the decision support system AQUATOOL at the basin scale. The water management model solves the allocation problem through network flow optimization and considers the environmental flows in some river stretches. Once volumes and flows are estimated, the water quality model is applied. Furthermore, the flows are evaluated from an ecological perspective using time series of aquatic species habitat indicators. This approach was applied in the Tormes River Water System, where agricultural demands jeopardize the environmental needs of the river ecosystem. Additionally, water quality problems in the lower part of the river result from wastewater loading and agricultural pollution. Our methodological framework can be used to define water management rules that maintain water supply, aquatic ecosystem and legal standards of water quality. The integration of ecological and water management criteria in a software platform with objective criteria and heuristic optimization procedures allows realistic assessment and application of environmental flows to be made. Here, we improve the general methodological framework by assessing the hydrological alteration of selected environmental flow regime scenarios.

Editor D. Koutsoyiannis; Guest editor M. Acreman

Citation Paredes-Arquiola, J., Solera, A., Martinez-Capel, F., Momblanch, A., and Andreu, J., 2014. Integrating water management, habitat modelling and water quality at the basin scale and environmental flow assessment: case study of the Tormes River, Spain. Hydrological Sciences Journal, 59 (3–4), 878–889.     

Short-term effects of changes in water management on the limnological characteristics and zooplankton of a eutrophic Mediterranean coastal lagoon (NE Iberian Peninsula)

The Ter Vell (NE Iberian Peninsula) is a eutrophic coastal lagoon which has been flooded by the excess irrigation water and the agricultural runoff during the last decades. Between 1999 and 2003, restoration measures were applied to improve its water quality. At the same time, but independently, agricultural water management drastically reduced the freshwater inflow. The short-term effects of these management actions on the limnological characteristics of the lagoon were analysed by comparing two hydrological cycles, one before (1999/2000) and the other one after (2002/2003) the actions. The two cycles are illustrative of opposite situations in the hydrological functioning of coastal wetlands. In the first, the lagoon was exorheic, with prolonged flooding periods and a low residence time; in the second, it had a more endorheic character, with scarce water inputs and prolonged periods of confinement. Consequently, nitrogen inputs diminished and organic load and salinity increased as the internal loading and the accumulation effects became more relevant. These effects were actually caused by the drastic reduction in the freshwater inflow which prevented, in turn, the success of the restoration measures. The zooplankton community of the Ter Vell lagoon was not significantly altered by the hydrological change, at least in the short-term, and rotifers and cladocerans, mainly those species indicative of eutrophy, dominated the community.